1. Field of the Invention
This invention relates generally to insulated coverings, specifically to a sleeping bag with batts that more effectively and economically provide increased insulation in a needed area.
2. Prior Art
A typical sleeping bag is constructed by sewing separate batts, or wide strips of insulation, one at a time onto a shell along straight quilt lines. Successive batts overlap preceding ones by half their width, so as to form two layers of insulation in a "shingle" arrangement. The distribution of the insulation is substantially even throughout the sleeping bag, i.e., it is two layers thick all around. However, an even distribution is inefficient, because a person's upper torso, which is the most critical area to keep warm, is not insulated any more than the lower torso or the legs. Increasing upper torso insulation by increasing the insulation of the entire bag is also inefficient, because the lower parts would be overly insulated, thus adding unnecessary weight and cost.
U.S. Pat. No. 4,090,269 to Hunt (1978) and 4,354,281 to Satoh (1982) show sleeping bags with parallel batts arranged transversely between inner and outer shells. The batts are evenly overlapped to provide two layers of insulation at all points on the sleeping bag. However, as stated, an even distribution of insulation is inefficient. Furthermore, two layers of insulation may not be enough for very cold climates.
U.S. patent to Roach (1990) shows a sleeping bag with parallel batts arranged longitudinally between inner and outer shells. The batts are overlapped to provide two layers of insulation at all points on the sleeping bag. However, again the even distribution of insulation is inefficient, and may not be enough for harsher climates.
It is also known that half batts, i.e., batts half the width of conventional batts, can be added to the upper torso area at intervals to provide more insulation. However, this is difficult and expensive to implement in production, because a worker must handle several different bulky batts simultaneously, and must remember the precise installation intervals of the full-width and half-width batts.
Insulated coverings similar to those proposed for sleeping bags have also been proposed for other garments. U.S. Pat. No. 1,393,975 to Rowley (1921) shows a continuous sheet of insulation folded back on itself three times at regular intervals to form elongated strips of insulation three layers thick. Although it provides greater insulation than two-layered coverings, it is difficult to manufacture, because folding a large sheet of thick insulation back and forth a great number of times is difficult and time consuming.